Javascript Regex: How to bold specific words with regex?

Question

Given a needle and a haystack... I want to put bold tags around the needle. So what regex expression would I use with replace()? I want SPACE to be the delimeter and I want

Answer 1

var needle = 'cows';

var regexp = new RegExp('(^|\s)('+needle+')(\s|$)', 'ig');

var old_string = 'cows at www.cows.com, milk some COWs';

var new_string = old_string.replace(regexp, '$1$2$3');